IEEE Solid-States Circuits Magazine - Summer 2020 - 26

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Feedback is an important instrument in the analog designers' toolkit. Additionally, in VCO-based
ADCs, feedback techniques demonstrate their value by improving
linearity as well as noise shaping.
Yet several published open-loop,
VCO-based ADC designs have comparable or even better performance
than do competing closed-loop designs, which is definitely the case
for ultrahigh-speed circuits.
For such open-loop, VCO-based
ADC circuits, feedforward and
digital calibration techniques are
the important enablers used to
boost linearity performance.
Oversampling, time-based chopping, and sensor embedding are
among the tricks used to improve
performance and power efficiency for sensing applications.
Although the core digital ring oscillator is well known, there have
been lots of circuit innovations
for VCO-based ADCs in recent
years, improving large-signal linearity and boosting speed.

Acknowledgments
This work was supported by the
Fund for Scientific Research Fland e r s ( B e lg i u m) a n d b y Sp a n i s h
Ministry of Science and Innovation
project TEC2017-82653-R (Spain).

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